Free File Camouflage is a free portable tool designed to hide a file inside a target image.
The interface has no particular surprises. Select some confidential file, a target image, enter the name of the image you'd like to create, an optional password, and you're done. Free File Camouflage opens the source file, encrypts it using AES, and tags the data onto the end of the destination image.
The end result is what looks like a regular JPEG image, and if anyone opens it with a graphics viewer they'll see the picture it contains, exactly as before.
But, if someone opens it with Free File Camouflage, they can use the De-Camouflage function to extract, decrypt and save a copy of the hidden file.
While most similar tools hide files within image data, Free File Camouflage takes a far more basic route, and just adds the encrypted file to the end of the JPEG.
This doesn't affect viewing - open the picture and it'll look entirely normal - but if an expert is looking closely at the files and their structure, there's more chance they'll realise something odd is going on.
Free File Camouflage should defeat non-technical users, though, and its simple approach does have another plus: there's no restriction on the size of file you can embed in an individual picture.